Method and apparatus for the disposal of waste sulphite liquor



July 24, 1956 H. D. SEYMOUR 2,755,749

METHOD AND APPARATUS FOR THE DISPOSAL OF WASTE SULPHITE LIQUOR FiledJuly 27, 1951 HEATER FLUE GAS /Z I AIR FUEL ELEVATOR scmaaw 5/ ASH BINAIR BLOWER L SULFHITE LlQUOR ST AM EVAPORATOR z THROTTLE VALVE INVENTOR.Hale D. Jeymour mww ATTORNEYS.

United States Patent METHOD AND APPARATUS FOR THE DISPOSAL OF WASTESULPHITE LIQUOR Hale D. Seymour, Western Springs, 11]., assignor to A.O. Smith Corporation, Milwaukee, Wis., a corporation of New YorkApplication July 27, 1951, Serial No. 238,923

9 Claims. (Cl. 110-7) The present invention relates to contactevaporation by solid heat transfer material and more particularly to aprocess for the evaporation and incineration of waste sulphite liquor orother liquids containing combustible material.

Sulphite liquor is a by-product in the production of wood pulp and paperby the so-called sulphite process. This spent liquor contains, inaddition to the sulphurous material, lignin and other soluble organicmaterials representing about fifty per cent of the wood originallyemployed.

The discharge of this waste sulphite liquor into streams and rivers hasresulted in a public nuisance due to the very harmful eifect of theliquor on the marine life in the streams. As a result, numerous methodshave been devised for the disposal of this liquor and the recovery ofthe valuable constituents therein. However, all of these disposalprocesses are expensive and require extensive equipment and as yet havenot proven economically A practical.

Heretofore the disposal process most frequently employed involved theevaporation of the waste liquor to approximately a 50% concentration ina suitable evaporator, followed by the transfer of the concentratedliquor to a furnace or boiler where it is burned. However, scaleformation on the heat transfer surfaces renders the evaporation processvery ineflficient because of the resultant low heat transfer rate. Inaddition, the burning of the concentrated liquor has presented seriousproblems in boiler tube maintenance and in release of fly ash.

The present invention is directed to a novel process for the disposal ofsulphite liquor whereby the waste liquor is preferably evaporated todryness, and the combustible portions of the evaporated liquor burned,in a continuous process. By this invention the difiiculties due to scaleformation are eliminated, for heat transfer in the evaporator isaccomplished by bringing the sulphite liquor into contact with acontinuously circulating mass of granular or pebbled heat transfermaterial which has been heated in a heater and is introduced into theevaporator as a continuous stream. The liquor is evaporated on contactwith the heated pebbles with the residue of evaporation tending toadhere to the surface of the pebbles. The pebbles are recirculated tothe heater where the combustible portion of the residue is burned fromthe surface of the pebbles, thus reheating the pebbles in preparationfor the recycling thereof.

An object of the present invention is to provide an inexpensive andrapid process for the disposal of sulphite liquor whereby theevaporation and incineration of the liquor may be accomplished in onecontinuous operation.

Another object is to provide a method of evaporating waste sulphiteliquor substantially to dryness by bringing the liquor into contact witha continuously moving mass of heated granular or pebbled solids.

Still another object is to provide a contact process for the evaporationand burning of liquids containing combustible matter whereby theevaporated liquid is burned to supply heat to contacting solids orpebbles during regeneration.

Other objects and advantages of the present invention will appear in thecourse of the following description.

In the drawing, the figure is a diagrammatic representation of theapparatus for the process to which the invention is directed.

Referring to the drawing, a solid heat transfer material, which may beany granular or pebbled refractory substance, is circulated in a closedcycle including a heater 1, an evaporator 2, and an elevator 3.

To start the cycle the heat transfer granules or pebbles are heated inthe heater 1 by any suitable means. As shown in the drawing the solidsare heated by the combustion of a mixture of fuel gas and air which isintroduced into the heater through line 4.

If the present invention is to be employed in the disposal of sulphiteliquor produced as a by-product in the wood pulp or paper industry, itmay be preferred to employ wood chips or shavings as fuel to heat thepebbles.

The highly heated pebbles pass through a feed leg 5 to the evaporator 2.

The temperature of the pebbles entering the evaporator may be in theneighborhood of 1500 to 2000 F. However this temperature may vary withina broad range with the desired temperature depending on the rate' offlow of the liquor entering the evaporator and the rate of flow of thepebbles being introduced into the evaporator.

A small amount of steam may be introduced into feed leg 5 by line 6 tocontrol the temperature of the pebbles entering the evaporator 2 and toprevent flow of gases or vapors between heater 1 and evaporator 2.

In the evaporator the pebbles take the form of a downwardly moving masswith heated pebbles continually being added to the top of the bed andthe cooled pebbles being continuously withdrawn from the bottom of thebed through feed chute 7 in the lower portion of evaporator 2.

The sulphite liquor is introduced into the evaporator 2 by line 8 andmay be sprayed, jetted through nozzles or cascaded over weirs onto thetop of the moving mass of pebbles. The sulphite liquor, as introduced,is normally a dilute by-product of the sulphite pulp making processcontaining approximately 10% of dissolved solids. However, concentratedliquor may be introduced as feed if desired, and the process of thepresent invention may be utilized to further concentrate and incinerateliquor having a concentration of over 50% solids which cannot beefiectively or economically evaporated by other evaporation systems. Inaddition to sulphurous constituents the dissolved solids consist oflignin, resins, and other combustible organic matter representing about50% of the wood originally employed in the sulphite process.

The sulphite liquor is evaporated on contacting the heated granules andthe low pressure steam produced during the evaporation operation leavesthe evaporator by line 9.

The temperature of the granules in the evaporator should preferably bemaintained below the temperature of decomposition of the organicmaterial in the liquor, so that the material will not decompose and bedriven 01f in the evaporation process with a resulting contamination ofthe steam. The steam produced may nevertheless tend to be somewhatcorrosive due to the presence of sulfur compounds and may be limited inapplication to process heating.

However the steam, whether corrosive or not, may be employed to stripsulfur dioxide from the sulphite liquor before the liquor is introducedinto the evaporator. By this operation a recovery of the essentialsulphur dioxide isattained and the steam produced by the evaporation ofthe stripped liquor will be correspondingly less corrosive.

,Any degree of evaporation maybe attained in the evaporator bypreferably controlling the temperature and rate of flow of the enteringgranules or by controlling the rate of flow of the entering liquor.

As a sulphite liquor having a concentration of greater than 50% solidswill generally burn without the addition of outside fuel, it isessential that the liquor be evaporated at least to such aconcentration. However, it may be most desirable to evaporate tocomplete dryness in order to subsequently obtain the most eflicientheating of the heat transfer pebbles in the heating section 1.

The temperature of the pebbles leaving the evaporator at chute 7 should.be just slightly above the evaporating temperature of the liquor inorder to obtain the maximum evaporating effect from each pebble, therebyreducing the amount of pebbles to be circulated in obtaining a givendegree ofevaporation. Further, a low evaporator exit temperatureconsiderably simplifies the, problems involved in design and maintenanceof throttle valve 10 in chute 7 and of elevator 3 which returns thepebbles to the heater 1 in that special heat resistant alloys are notrequired for the throttle valve and the elevator.

As the sulphite liquor is evaporated, the residue of evaporation,consisting of the sulphurous and organic compounds, tends to deposit onthe surface of the refractory pebbles. The coated pebbles and anyevaporation residue which has not adhered to the pebbles, movedownwardly through the evaporator and are discharged therefrom throughfeed chute 7 and throttle valve 10 to elevator 3. The throttle valve 10controls the rate of flow of the pebbles through the system.

The elevator 3 is employed to lift the pebbles and the evaporationresidue to heating chamber 1 and may comprise any convenient means suchas a bucket lift or air lift:

From the top of the elevator 3 the coated pebbles and freeresidue flowdownwardly through feed chute 11 to heater 1 where the free residue andthe residual deposit on the pebbles are burned to pre-heat or partiallypreheat the pebbles. Additional fuel may be introduced into the heateras hereinbefore described to further heat the pebbles to the desiredre-cycling temperature. The resulting combustion gases leave-the heaterthrough flue 12. During the heating, the pebbles in the heater 1 are inthe form of a downwardly moving mass, and by the time the pebbles reachthe bottom of the heater the coating has been burned from the pebblesand the pebbles are heated sufficiently to enter theevaporator 2.

To reduce the heat loss in the heater through the flue gases, it may bedesirable to operate the heater at a temperaturejust above the lowesttemperature at which the combustibles will ignite. This relatively lowoperating temperature in the heater will simplify design problems andreduce the cost of that part of the unit. However, the low operatingtemperature in the heater results in the pebbles having a lowertemperature as they enter the evaporator, and hence decreases theevaporating effect of eachpebble. Thus a greater volume of lowtemperature pebbles will have to be circulated through the system toproduce the equivalent evaporating effect obtained by higher temperaturepebbles. Therefore, it is necessary to balance these factors, with theoperatrngtemperature of the heater being dependent upon the economics ofmanufacture.

As a considerable amount of ash is produced by the combustion of theevaporation residue in the heater 1 and as there is some noncombustibleresidue, a means may be provided in the system for the removal of theash and noncombustible residue.

The ash and noncombustible residue are readily separable from the heattransfer pebbles, and separation may be accomplished by setting feed leg5 at an angle to the heater 1 and inserting a screen or perforatedseparator 13 into the portion of the feed leg that faces downward. Asthe heated pebbles, ash and noncombustible residue pass downwardlythrough the leg, the ash and residue will fall through screen 13 intoash bin 14, and the pebbles, being too large to pass through screen 13,will continue to evaporator 2. Any ash or residue not removed from thesystem merely serves as additional heat transfer material.

The present invention utilizes the combustible products in sulphitewaste liquor to provide approximately 60 to 70% of the heattheoretically required to evaporate the liquor to dryness. By utilizingthe flue gases and the steam generated in the evaporator for processheating, the process may tend to approach an overall thermal equilibriumwhereby the heat generated by the additional fuel added in the heater isbalanced by the heat recovered from the flue gases and from thegenerated steam.

The present invention may be applied to the evaporation of any liquidand is particularly adapted for use in the evaporation of liquidscontaining solid matter, whereby the evaporation solids or residue maybe recovered as such, or, the combustible portion of the residue may beutilized to pre-heat the refractory pebbles.

Although the present invention has been described as a continuousprocess of evaporation and incineration, it is contemplated that a batchprocess may also be employed for smaller quantities of liquor, whereby acharge of liquor is introduced onto a stationary bed of heated pebblesand evaporated, with the evaporation residue being burned in the sameconfined zone to re-heat the pebbles.

Various practices and embodiments of the invention may be employedwithin the scope of the following claims.

I claim:

1. A process for the continuous evaporation and in cineration of wastesulphite liquor comprising, preheating a divided solid heat transfermaterial in a confined burning zone to a temperature above that requiredto evaporate the liquor, passing the divided solid heat transfermaterial through a confined evaporating 'zone as a moving mass,introducing said liquor into said evaporating zone into contact with theheat transfer material to evaporate said liquor with a portion of theevaporation residue being deposited on said heat transfer material,withdrawing the vaporous products of evaporation from said evaporatingzone, separately withdrawing the heat transfer material and theevaporation residue from said evaporating zone with the temperature ofsaid withdrawn material being maintained slightly above the evaporationtemperature of said liquor to obtain the maximum evaporating effect fromsaid material, transferring said material and said residue to theburning zone, passing the heat transfer material through said burningzone as a moving mass and passing fuel and oxygen to the material in theburning zone and igniting the same with the combustible portion of theevaporation residue being burned in contact with said material to raisethe temperature of said material, withdrawing the combustion gases fromsaid burning zone, and returning the substantially residue free materialagain to the evaporation zone to restart the process cycle.

2. A process for the continuous evaporation and incineration of sulphiteliquor comprising, preheating a divided solid heat transfer material toa temperature above the temperature required to evaporate the liquor,passing the heated divided solid heat transfer material through aconfined evaporating zone as a downwardly moving mass, introducing theliquor into said evaporating zone into contact with the moving mass ofheat transfer material to evaporate said liquor, withdrawing thevaporous products of evaporation from the top of said evaporating zone,separately withdrawing the heat transfer material together withevaporation residue from the bottom of said evaporating zone,transferring said material and said residue to a confined burning zone,passing said material and said residue through said burning zone as amoving mass introducing a combustion supporting medium into the burningzone and igniting the combustible portion of the residue to therebyraise the temperature of said material, withdrawing the combustion gasesfrom said burning zone, and returning the substantially residue freematerial again to the evaporation zone to restart the process cycle.

3. A process for the continuous evaporation and incineration of liquidscontaining combustible material, comprising, preheating a divided solidheat transfer material to a temperature above the temperature requiredfor the evaporation of the liquor, passing the divided solid heattransfer material through a confined evaporating zone as a moving mass,introducing said liquor into said evaporating zone into contact With theheat transfer material, Withdrawing the vaporous products of evaporationfrom said evaporating zone, transferring the heat transfer material andthe residue of evaporation to a confined burning zone, passing fuel andoxygen to the material in the burning zone and igniting the fuel to burnthe combustible portion of said residue in contact with the heattransfer material and simultaneously raise the temperature of saidmaterial, withdrawing the combustion gases from said burning zone,separately removing the noncombustible residue and the ash produced bythe burning from said burning zone, and returning the substantiallyresidue free material again to the evaporation zone to restart theprocess cycle.

4. A process for the continuous evaporation and incineration of liquidscontaining combustible material comprising, preheating a divided solidheat transfer material in a confined burning zone to a temperature abovethe temperature required to evaporate the liquid, passing the solid heattransfer material from the burning zone through a confined evaporatingzone as a heated moving mass, introducing said liquor into saidevaporating zone into contact with the heat transfer material toevaporate said liquor substantially to dryness, withdrawing theresulting vaporous products from said evaporating zone, transferring theheat transfer material and the residue of evaporation to the burningzone, introducing fuel and a combustion supporting medium to thematerial in the burning zone and igniting the fuel to burn thecombustible portion of said residue in contact with the heat transfermaterial and simultaneously raise the temperature of said material,withdrawing the combustion gases from said burning zone, separating thenoncombustible residue and ash produced by the burning of said residuefrom the heat transfer material, and returning the substantially residuefree material again to the evaporation zone to restart the processcycle.

5. A process for the continuous evaporation and incineration of wastesulphite liquor comprising, preheating a granular solid heat transfermaterial in a confined burning zone to a temperature above theevaporation temperature of the liquor by introducing fuel and oxygeninto said burning zone and igniting the same, passing the granular solidheat transfer material from the burning zone through a confinedevaporating zone as a continuously moving mass, controlling thetemperature of the heat transfer material entering the evaporating zoneby passing steam through said material before said material isintroduced into said evaporating zone, introducing said liquor into saidevaporating zone into contact with the heat transfer material toevaporate said liquor with a portion of the evaporation residue beingdeposited on the surface of said heat transfer material, withdrawing thevaporous products of evaporation from said evaporating zone, separatelywithdrawing the heat transfer material containing the deposited residuetogether with undeposited residue from said evaporating zone,transferring said material and said residue to the burning zone, passingfuel and oxygen to the material in the burning zone and igniting thesame to burn said residue in said burning zone and raise the temperatureof said material, Withdrawing the combustion gases from saidburningzone, and returning the substantially residue free material againto the evaporation zone to restart the process cycle. 7

6. A closed cycle apparatus for the evaporation and incineration ofWaste sulphite liquor comprising, an evaporator having an inlet and anoutlet for the entry and discharge respectively of a solid transfermaterial and having a second inlet for the introduction of the sulphiteliquor, said liquor adapted to be introduced into contact with a heatedmass of divided solid heat transfer material to evaporate said liquorwith the residue of evaporation having a concentration of at least 50%solids, a heater disposed above the evaporator for burning said residuein contact With the heat transfer material to raise the temperature ofsaid material, means communicating with said heater for introducingadditional fuel and a combustion supporting medium to the heater withsaid fuel being burned in said heater in contact with the heat transfermaterial to further raise the temperature of said material, elevatormeans connecting the outlet of said evaporator to the upper portion ofsaid heater to convey the heat transfer material and the residue ofevaporation from the evaporator to the heater, a feed leg connecting thelower portion of said heater to said first named inlet of saidevaporator to conduct the heat transfer material and the uncombustibleportion of said residue from the heater to the evaporator, and means forseparating the uncombustible portion of said residue from the heattransfer material prior to the introduction of said material into theevaporator.

7. An apparatus for the evaporation and incineration of liquidscontaining combustible solid matter comprising an evaporation chamberwherein the liquid is adapted to be evaporated by contact with a dividedsolid heat transfer material with said material being at a temperaturesubstantially above the temperature required for the evaporation of saidliquid, conveying means for introducing said heat transfer material intosaid chamber, means for introducing said liquid into said chamber, meansassociated with said conveying means for controlling the temperature ofthe material entering said evaporation chamber, and means for burningthe combustible portion of the residue of evaporation to re-heat theheat transfer material.

8. In a process for the evaporation and incineration of liquidscontaining solid combustible matter, the steps comprising, preheating abed of solid heat transfer material to a temperature substantially abovethe temperature required for the evaporation of the liquid, contactingthe liquid by the bed of solid heat transfer material in an evaporationzone to evaporate the liquid and deposit the residue products ofevaporation on said material, withdrawing the material from theevaporation zone, heating the material by passing oxygen to the materialin a burning zone and igniting the combustible matter of the residue toburn the residue from the material and simultaneously heat said materialto the temperature required for evaporation of additional liquid, andthen returning the heated and generally clean heat transfer materialinto contact with the additional liquid that is supplied for evaporationand incineration.

9. In a process for the continuous evaporation and incineration of wastesulphite liquor, the steps comprising heating a divided solid heattransfer material in a confined burning zone to a temperaturesubstantially above the temperature required for the evaporation of theliquor by introducing fuel and oxygen into said burning zone andigniting the same, passing the divided solid heat transfer material fromthe burning zone through a confined evaporating zone, introducing theliquor into said evaporating zone into contact with the material toevaporate said liquor with a substantial portion of the evaporationresidue being deposited on the surface of the material, withdrawing thevaporous products of evaporation from said evaporating zone, separatelywithdrawing the heat transfer material containing the deposited residuetogether with any undep'osited residue from said evaporating zone,transferring said residue coated material and the undeposited residue toa burning and heating zone, passing said material through the burningand heating zone as a moving mass and passing fuel and oxygen to thematerial in the burning and heating zone and igniting the same to burnthe combustible portion of the residue on the material together with theundeposited residue to thereby remove the residue from the material andsimultaneously raise the temperature of said material above thatrequired to evaporate said liquor, withdrawing the combustion gases fromthe burning and heating zone, and

returning. the substantially residue free material again (0 theevaporation zone to restart the process cycle.

References Cited in the tile of this patent UNITED STATES PATENTS424,755 -Blackmail Apr. 1, 1880' 478,980 Blackman July 19, 18921,738,890 Goodrich Dec. 10, 1929 2,303,717 Arveson Dec. 1, 19422,374,151 Wolk Apr. 17, 1945' 2,393,893 Evans Jan. 29, 1946 2,501,977Wailerstedt Mar. 28, 1950

2. A PROCESS FOR THE CONTINUOUS EVAPORATION AND INCINERATION OF SULPHITELIQUOR COMPRISING, PREHEATING A DIVIDED SOLID HEAT TRANSFER MATERIAL TOA TEMPERATURE ABOVE THE TEMPERATURE REQUIRED TO EVAPORATE THE LIQUOR,PASSING THE HEATED DIVIDED SOLID HEAT TRANSFER MATERIAL THROUGH ACONFINED EVAPORATING ZONE AS A DOWNWARDLY MOVING MASS, INTRODUCING THELIQUOR INTO SAID EVAPORATING ZONE INTO CONTACT WITH THE MOVING MASS OFHEAT TRANSFER MATERIAL TO EVAPORATE SAID LIQUOR, WITHDRAWING THEVAPOROUS PRODUCTS OF EVAPORATION FROM THE TOP OF SAID EVAPORATING ZONE,SEPARATELY WITHDRAWING THE HEAT TRANSFER MATERIAL TOGETHER WITHEVAPORATION RESIDUE FROM THE BOTTOM OF SAID EVAPORATING ZONE,TRANSFERRING SAID MATERIAL AND SAID RESIDUE TO A CONFINED BURNING ZONE,PASSING SAID MATERIAL AND SAID RESIDUE THROUGH SAID BURNING ZONE AS AMOVING MASS INTRODUCING A COMBUSTION SUPPORTING MEDIUM INTO THE BURNINGZONE AND IGNITING THE COMBUSTIBLE PORTION OF THE RESIDUE TO THEREBYRAISE THE TEMPERATURE OF SAID MATERIAL, WITHDRAWING THE COMBUSTION GASESFROM SAID BURNING ZONE, AND RETURNING THE SUBSTANTIALLY RESIDUE FREEMATERIAL AGAIN TO THE EVAPORATION ZONE TO RESTART THE PROCESS CYCLE.